Service chaining involves the interception of traffic (packets/frames) and steering them through an ordered set of service functions. Traffic is intercepted through the use of a classifier function at a network node for steering through the service functions. Traffic steering the traffic from the classifier through the service functions is performed by use of a service overlay in the network. This service overlay provides a provision for carrying service metadata in addition to the original packet.
The service chain and the corresponding forwarding state is constructed, maintained and distributed by a control-plane (centralized or distributed). Service chain construction involves establishment of a binding between forwarding state and the service chain. This mapping of forwarding-state to the service chain is termed the service path.